One definition of epic given by merriam-webster.com is the following: "extending beyond the usual or ordinary especially in size or scope".
So, is there a song that fits such definition?
I believe so.
What song is most frequently featured in literature, movies and TV shows?
What song is featured in Harriet Beecher Stowe's novel Uncle Tom's Cabin?
What song was sung by the Cherokees as they walked on the Trail of Tears?
What song has been performed in concerts at Carnegie Hall?
What song was sung during the USA's Civil Rights marches of the 1960s?
What song was featured at the Woodstock Music Festival?
What song was performed by American musicians opposed to the Vietnam War?
What song was recorded by Aretha Franklin, Rod Stewart, Elvis Presley?
What song was featured in an episode of The Simpsons (American TV show)?
What song was performed at a rock concert for Nelson Mandela's 70th birthday?
What song is described by British music journalist Steve Turner as "a song that could be sung by young and old, Republican and Democrat, Southern Baptist and Roman Catholic, African American and Native American, high-ranking military officer and anticapitalist campaigner."
What song has what is perhaps the most-recognized melody throughout the world?
star spangled banner
I believe fits this bill....where's my prize????

Why would "The Star Spangled Banner" be recorded by Rod Stewart and be performed at a celebration of Nelson Mandela's 70th birthday?
Try again.

so I gather you think I'm beig a little etnocentric
"happy birthday" then
I hadn't thought of "Happy Birthday" as being an epic song, but it also fits the definition of
epic. Thanks!
By the way, as the OP says, "There is no wrong answer."
However, I want to illustrate the difference between a song that is popular with a particular generation or nationality and a song that spans across generations and nationalities.
"Happy Birthday" is one such song.
Another song is what I describe in my first post.